Importance: Depression is one of the most common mood disorders worldwide and an important public health concern. A large fraction of depression patients fails to respond to the current treatment. Thus, exploring novel pathophysiology of depression is important for the identification of biomarkers for novel targeted-treatment modalities. Inflammation, a process increased in human aging, has been widely suggested to have a significant influence in the pathophysiology of depression. Therefore, studying inflammatory profiles and their association with depressive symptoms is valuable in contributing future ability to early diagnose, treat and possibly prevent depression.
Objective: To determine whether LPS-induced monocyte expression of intracellular cytokines is a sensitive measure of inflammation that can be correlated to depressive symptoms.
Design: Cross-sectional, secondary analysis of data from the Sleep Health Aging Research (SHARE) project
Setting: Los Angeles community
Participants: 180 community-dwelling older adults (>60 years old) with proportionate representation from high and low socially isolated groups.
Main Measures: LPS-induced IL-6 and TNF-a expression in isolated peripheral blood monocytes was measured by flow cytometry. Depressive symptoms were measured using the 10-item Center for Epidemiological Studies-Depression Scale (CES-D 10).
Covariates: age, sex, ethnicity, education, BMI, Charlson Comorbidity index
Results: In an overall analysis of the sample, we found no statistically significant correlation between depressive symptoms and LPS-induced expression of pro-inflammatory cytokines: delta TNF-a (p>0.05, adjusted B = 0.040), delta IL-6 (p>0.05, adj. B = 0.082), delta TNF-a + IL-6 (p>0.05, adj. B=0.078).
Conclusion: Although our data is not statistically significant, measuring inflammation via LPS-induced intracellular cytokine expression remains a topic of interest for further study. Our sample was a largely healthy population with low depression scores. In the future, in addition to obtaining a larger sample size, more sensitive measures of depression will be needed in order to more accurately associate pro-inflammatory cytokines with depressive symptoms in older adults. Furthermore, designing a prospective cohort study will be beneficial in order to associate cytokine levels with depression outcomes.